Dropdown menu from Dessign ‘Studio responsive theme’

Help please!
I am using this theme https://dessign.net/studio-responsive-theme/ and need help in changing the font on the dropdown menu. At the moment i’ve managed to add Courier to all the website, but yet every effort to change the menu has failed.

A)Ive tried using googlefonts plugin. I heard about trying to add another drop down meny option and to try and override the theme by going Settings > Google Fonts > Add CSS selectors but i don’t know what CSS selector text to add….

B) Ive also tried pasting into the custom CSS in the customizing box…
#nav-second ul.sf-menu a {
color: #fff;
font-family: Courier, monospace;
font-size: 18px;
}
#nav-second ul.sf-menu a:hover {
background: #333;
color: #eee;
}
#nav-main ul.sf-menu ul li a {
font-size:20px;font-family: Courier, monospace;
}

If anyone can help me that would be AMAZING!!! CSS, google fonts…anything!!

thanks in advance
??

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